Tuesday, February 07, 2006

10K Ohm resistors burned again

It's weird that the 10K Ohm resistors were burned again. This time were second resistor and third one. The current must be drained too much somewhere, so that the resistors were burned again and again. We measured the current which passed through the whole system, here we named it Imon. Now Imon only can keep about 300 milliseconds. I also measured the firing angle from Box 2270, that waveform looks strange, too.

I found some waveforms which were recorded on Jan 10th, 1995. The current should be kept about 800 milliseconds, and the firing angle looked like a flat pulse. From those pictures, there was one waveform mostly like the above one, it marked "Drawing high current". There was another note on the other waveform, "Swayback should not be here. Indicate I separate changing cycles due to only 1/2 of the SCR firing block working".

We already checked the 2155 circuit board in the box today, it's very good. We will check the 2154 board, which generate the firing angle signal.